The present invention relates to test head assembly for a test system.
Electronic devices, such as integrated circuits (ICs), are normally tested after production and before use. As an example of a test system generally applied for testing purposes, automatic test equipment (ATE) is designed to conduct analysis of functional or static parameters to evaluate the degree of performance degradation and may be designed to perform fault isolation of unit malfunctions. The decision making, control, or evaluative functions are normally conducted with minimum reliance on human intervention.
FIG. 1A illustrates, in a generalized cross sectional view, a typical test system as known in the art, such as the Hewlett-Packard HP 83000 or HP 95000 series. For testing a device under test (DUT) 20, the test system 10 comprises a tester 30 and a test head assembly 35. The test head assembly 35 represents the mechanical and electrical interface between the DUT 20 and the tester 30. The tester 30 generally comprises test electronic for generating test signals and evaluating signals received from the DUT 20.
The test head assembly 35 comprises a test head 40 and at least one DUT board 60. The DUT 20 might be fixed directly or via a socket 50 to the DUT board 60, which, again, is normally mechanically fixed to the test head 40 by means of a fixture 70.
The DUT board 60 represents the mechanical and electrical interface between the DUT 20 and the test head 40. The DUT board 60 is also employed to adapt electrical contacts from the DUT 20 to electrical contacts at the test head 40. In particular with respect to miniaturized ICs, the necessity of such an adaptation of the miniaturized contacts of the DUT 20 to larger contacts of the test head assembly 35 becomes readily apparent.
The fixture 70 is employed for mechanically holding and fixing the DUT 20 via the DUT board 60 to the test head 40 and to allow exchanging the DUT board 60.
FIG. 1B illustrates, in an explosive side view, a typical principle for fixing the DUT board 60 to the test head 40, as employed e.g. in the Hewlett-Packard. HP 83000 or HP 95000 series. The DUT board 60 can be mechanically affixed to the test head 40 by means of a plurality of screws 80, whereby a stiffener-90, as part of the fixture, can be arranged therebetween. When the DUT board 60 is mechanically affixed to the test head 40, one or more contact areas 95A, 95B and 95C of the test head 40 electrically couple to contact areas 100A, 100B and 100C of the DUT board 60.
The contact areas 95A, 95B and 95C comprise a plurality of pins (not shown in detail), such as spring loaded pins, which will be forced/pushed against respective contact pads 110 (shown in FIGS. 2) of the.contact areas 100A, 100B and 100C of the DUT board 60 for providing a good electrical contact. Since the DUT boards 60 are generally formed of flexible plastic material, the stiffener 90 is employed for avoiding bending of the DUT board 60 under the influence of the contact pressure.
While the DUT board 60 in FIG. 1B is affixed to the test head 40 by means of mechanical connecting means such as the screws 80, FIG. 1C illustrates another principle wherein the DUT board 60 is affixed to the test head 40 by means of negative pressure means as employed e.g. in the Teradyne Integra series J750. The top part of FIG. 1C shows a cross sectional view, while the lower part depicts a worm eye""s view from the direction of arrows A. Vacuum slots 120 in the test head 40 are arranged close to the contact areas 100A and 100B for-removing air. Rubber seal lips 130A and 130B are provided for establishing a negative pressure between the DUT board 60 and the test head 40, thus attaching the DUT board 60.
It is to be understood that, in general, for each different DUT 20 a specific and thus different DUT board 60 has to be provided for adapting the specific layout of contacts of the respective DUT 20 to the contact areas 95 provided from the test head 40. Employing exchangeable DUT boards 60 renders the test system 10 capable for testing a plurality of different DUTs 20. It is clear that different test algorithms may have to be provided by the tester 30 for any different DUT 20.
FIGS. 2A to 2D show examples of DUT boards 60 as known in the art. The one or more DUTs 20 are generally located in the center of the respective DUT board 60. It is clear that number of DUTs 20 on one respective DUT board 60 is limited by the sizes and/or pin counts (i.e. the number of pins or other individual electrical contacts) of the respective DUTs 20, the pin count (channels) of the test head 40, and the available area in the center of the DUT board 60. Each DUT board 60 comprises one or more contact areas 100 comprising a plurality of individual contact pads 110 electrically coupled to the (one or more) DUT 20, preferably via strip conductors of the DUT board 60.
When the DUT board(s) 60 is/are fastened to the test head 40, individual contact areas 95 of the test head 40 couple to the respective contact areas 100 for providing an electrical contact between the test head 40 and the DUT(s) 20. Spring-loaded cable assemblies designed in accordance with the respective contact areas 100 couple thereto for establishing the electrical contact, between the respective DUT boards 60 and thee test head 40.
Changing between different DUTs 20, however, generally requires a change in the hardware, of the test head assembly 35 adapted to the specific arrangement of DUTs 20 and their respective contact areas 100. In most cases, however, only the respective DUT boards 60 have to be exchanged. FIGS. 2A and 2B illustrate center arrangements of the DUT board 60. The DUT board 60 in FIG. 2A comprises four contact areas 100A, 100B, 100C and 100D substantially arranged around the DUT 20. An example of an embodiments according to FIG. 2A can be found e.g. in the Hewlett-Packard HP 83000 Series. In FIG. 2B, only one contact area 100 is provided which substantially encircles the DUT 20. An embodiment according to FIG. 2B can be found e.g. in the Teradyne J971 or Schlumberger S9000 series. The center arrangements of FIGS. 2A and 2B are mainly used for optimizing timing delay requirements in that the contact area 100 is designed in a way that the individual contacts thereof are located as close as possible to the corresponding contacts of the DUT 20.
FIG. 2C shows a device-specific arrangement for a plurality of individual (i.e. physically separated) DUT boards 60. Each DUT 20 is located in the center of a respective DUT board 60, whereby only one DUT 20 is applied on each DUT board 60. The contact area 100 of each DUT board 60 is device-specific and may substantially correspond to the centered arrangement according to FIG. 2A, An example of an embodiment according to FIG. 2C can be found in the Hewlett-Packard HP 95000 Series. The device-specific arrangement according to FIG. 2C in particular fits the requirements of short timedelay and multi-site testing.
FIG. 2D shows a DUT board 60 designed for the specific requirements of the negative pressure attachment systems as depicted in FIG. 1C. One or more DUTs 20 are arranged in a row between parallel contact areas 100.
It has to be understood and it is expressly noted that the different attaching systems as depicted in FIGS. 1C and 1D require entirely different solutions for the design of the, DUT board 60. Whereas the mechanical connecting system according to FIG. 1B allows to arrange a plurality of individual DUT boards 60 as shown in FIG. 2C, the negative pressure attachment system of FIG. 1C requires that all DUTs 20 have to be located on one single. DUT board 60 since the negative pressure applied through the vacuum slots 120 requires an uninterrupted space between the contact areas 95 and 100. A separation into individual DUT boards 60 would require a modification of the negative pressure applying means arranged in the test head 40. Such modifications at the test head 40, however, are normally very expensive and would require a detailed knowledge of the spatial dimensions of the specific arrangement of individual DUT boards 60.
Each of the designs of the DUT boards 60 in the FIGS. 2A-2D requires a specific design of parts corresponding to the DUT boards 60 of either or both the fixture 70 and the test head 40. This limits the exchangeability of different DUT boards 60 or requires costly modifications of corresponding parts at the test head site.
It is an object of the present invention to provide a more flexible test head arrangement allowing an easy exchange of different DUT boards.
According to the invention, a test head assembly for a test system comprises a test head having a plurality of test head contact areas, each with one or more individual contacts, for providing electronic signals to one or more devices under testxe2x80x94DUTxe2x80x94and/or for receiving electronic signals therefrom. The test head assembly further comprises fastening means for fastening one or more individual, physically separated DUT boards to the test head, each DUT board being provided for holding one or more of the DUTs and adapting electrical contacts thereof to at least one of the plurality of test head contact areas.
In order to provide a flexible and modular test head arrangement allowing an easy exchange of different DUT boards with different seizes, the arrangement of the fastening means and the plurality of test head contact areas is commensurable, so that one or more DUT boards with same and/or different lateral dimensions are attachable to the test head.
In a first preferred embodiment, the arrangement of the fastening means and the plurality of test head contact areas is commensurable in (only) one dimension (e.g. in the direction of the breadth of the DUT boards), so that one or more DUT boards with same and/or different seizes in that dimension can be attached to the test head preferably in a longitudinal row. Accordingly, the arrangement can provide and support more than one longitudinal rows, preferably arranged as substantially parallel rows, so that in each row one or more DUT boards with same and/or different seizes (e.g. breadths) in that dimension can be attached.
In the first embodiment the fastening means and the plurality of test head contact areas are preferably arranged in one or more longitudinal rows. Preferably, each DUT board comprises at least one DUT contact area having one or more individual contacts electrically coupled to the one or more DUTs of that respective DUT board. Each DUT contact area can be electrically coupled to at least one of the plurality of test head contact areas for providing an electrical contact between the respective DUT board and the test head, and each DUT contact, area is arranged substantially parallel to the one or more longitudinal rows.
In a second preferred embodiment, the arrangement of the fastening means and the plurality of test head contact areas is commensurable in two dimensions (e.g. in the direction of the breadth and the length of the DUT boards), so that one or more DUTT boards with same and/or different seizes in one or both of that two dimensions can be attached to the test head.
In the second preferred embodiment the fastening means and the plurality of test head contact areas are preferably arranged in accordance with the first embodiment. The second preferred embodiment, however, further comprises adapting means for adapting the test head contact areas to be coupled to a respective DUT board to the lateral dimensions of each DUT board. Preferably, the adapting means allow/s to either withdraw one or more test head contact areas from contacting the respective DUT board, or to couple only one or more test head contact areas to the respective DUT board.
The second preferred embodiment preferably provides a certain redundancy of fastening means and test head contact areas, so that a great variety of DUT boards with different lateral dimensions can be coupled to the test head.
It is clear that the respective DUT boards according to the invention have to be adapted to the test head assembly to be coupled to, so that the respective DUT contact areas are adapted to match with corresponding ones of the plurality of test head contact areas. This can be preferably accomplished by arranging the DUT contact areas in a predefined way, e.g. only in one or more parallel rows with defined distances between those rows, whereby the arrangement of the DUT contact areas substantially corresponds with the arrangement of the plurality of test head contact areas, e.g. with defined distances substantially match with defined distances between one or more parallel rows of the plurality of test head contact areas whereby the distances between the rows of the DUT contact areas and the test head contact areas substantially match.